1. Field of Invention
The present invention relates to a method for recovering valuable metals contained in ore by way of leaching and dissolving the ore in the aqueous solution to recover the objective metals. More specifically, the present invention relates to leaching copper and gold and separating and recovering them in serial steps.
2. Background Technique
Copper from copper-sulfide ore among the ores is recovered by a smelting method, in which the ore is smelted at a temperature usually exceeding 1000 degree C., and the impurities, particularly iron, are fixed in the slag and are separated from the copper. In the smelting process, the refined copper sulfide (Cu2S) referred to as the copper matte is yielded, and the noble metals concentrated in the copper matte are subsequently recovered. In the smelting process, since sulfur of the copper-sulfide ore is gasified in the form of sulfur dioxide, it must be subjected to the waste gas treatment. In addition, a refining process at a high temperature is carried out after smelting. A large amount of fuel is, therefore, consumed in the post-smelting refining process. Furthermore, when the impurity level of raw material becomes high, the amount of reverts increases so much that the treatment efficiency is lowered. The ore capable of smelting has a certain limited ratio of sulfur to copper. Processing efficiency of the raw material having low copper grade is disadvantageously low.
Various hydrometallurgical processes for treating the copper-sulfide ore in aqueous solution have been developed to eliminate such drawbacks involved in the smelting as waste-gas treatment, a large fuel consumption, and the limitations of impurities and copper grade of raw material. A hydrometallurgical process for recovering copper from the copper ore and the like is established with regard to the sulfuric-acid leaching. This leaching is combined with solvent extraction and electrowinning and is referred to as an SX-EW. Commercial plants of SX-EW have been operated in practice.
However, the copper ore, which can be leached in the sulfuric acid bath is, the one mainly consists of oxide, since sulfuric acid leaching of copper sulfide is disadvantageous in slow leaching speed, low leaching ratio and difficult recovery of precious metal. SX-EW is not commercially carried out with regard to the copper concentrate, the copper grade of which is enhanced by dressing.
Proposal to avoid the operation at high temperature and high pressure have also been made to enhance the leaching ratio of copper by using the halide solution. However, quality of copper recovered in the halide solution is poor. An electrolytic tank for recovering the copper in the halide bath is complicated in structure.
When one compares the smelting process and hydrometallurgical process, it is noticeable that precious metal behaves in a different manner. The precious metal is difficult to recover in the hydrometallurgical process. In the hydrometallurgical process, the copper dissolved in the solution is recovered, while the leach residue containing the precious metal is re-treated for recovering. The yielded leach residue is in a large amount and contains a few tens g/t of precious metal, a few thousands g/t of unleached copper, and a considerably larger amount of unleached iron. These grades of metals necessitate to consume a large amount of reagents for recovering precious metal. For example, cyanide is usually used for leaching gold, since a cyanide forms a stable complex with gold. However, since the cyanide also forms stable complexes with copper and iron, a huge amount of the cyanide is consumed, when it is used for leaching the residue mentioned above. In addition, since a cyano specie is toxic, sodium cyanate, which is stable, is usually used. However, cyano gas is easily formed from the sodium-cyanate solution, when the acid concentration rises. It is, therefore, necessary to extremely strictly control the leaching solution. In addition, the location, where a plant using the sodium-cyanide solution is permitted to build, is being limited.
AU Patent No. 669906 entitled as “Production of Metals from Minerals” (hereinafter referred to as Patent Document 1) and AU patent application 2003287781 entitled as “Recovering Metals from Sulfidic Materials” (hereinafter referred to as Patent Document 2) propose a hydrometallurgical method employing neither high temperature nor high pressure. In these methods, the sulfide ore is leached in a halide bath based on the aqueous chloride solution. Gold is recovered as well. In the method of Patent Document 1, acidic Cl—Br based electrolyte solution, which has high oxidation-reduction potential and contains copper in the form of Cu2+, is reverted to the copper leaching process of the sulfide ore. Air is blown into the leach liquor, with the result that Cu1+ is leached from the sulfide ore. The copper in cuporus state electrowinning is then carried out. However, the halide, that is, a halex, typically BrCl2−, used in this method for leaching is difficult to handle and is harmful. Special oxidizing agent such as oxygen, halogen gas, e.g., chlorine gas, or the like, must be used to enhance the leaching ratio of gold. In addition, since the electrowinning of copper is carried out using chloride bath, the electrolytic copper is of poor quality and must be subjected to expensive refining. Furthermore, an electrowinning plant is complicated, and its maintenance is disadvantageously difficult.
CA Patent 1105410 entitled as “Method of Obtaining Copper From Sulphurized Concentrates” proposes to produce a high-quality copper, by a method comprising the steps: leaching the copper concentrates in the halide bath; extracting the copper ions of the halide bath into the organic solvent; separating the organic phase and the aqueous phase; then bringing the organic phase into contact with the sulfuric acid to convert the copper to the copper sulfate; and, electrowinning by way of a conventional sulfuric acid bath. The electrolytic copper obtained has improved quality. In this method, chalcopyrite is leached and successively an air-blowing step for oxidizing the copper in cuporus state to the copper in cupric state is carried out. The liquor in the oxidizing step is reverted to leaching step. Although the copper can be leached, disadvantageously, the gold contained in the copper concentrate cannot be leached. At present, it is difficult to treat ores in a large scale by the hydrometallurgical process using the halide, in the light of cost and management. Mining developments at present are not based on the hydrometallurgical process using the halide bath.